1. Field of the Invention
Invention relates to an orthodontic bracket and process for mounting the same of the type which is directly bonded to the surface of a tooth by glueing with a dental cement. More particularly, the invention relates to an apparatus and process for directly bonding the posterior surface of the base of an orthodontic bracket to the front surface of the tooth in which a glue-line is produced having a predetermined thickness.
2. Description of the Prior Art
In recent years it has become common place to directly bond the posterior surface of the base of an orthodontic bracket to the front surface of a tooth by glueing with a dental cement. Numerous cements have been developed which have different bonding properties which necessitate the attainment of a glue-line thickness having a predetermined thickness to produce a glue joint of optimum strength. For example, one type of well known dental cement used for direct bonding orthodontic brackets requires a glue-line thickness ranging from 0.003 inches to 0.007 inches to produce the maximum strength bond. Whereas another well known dental cement produces its maximum bond strength with a glue-line thickness of 0.020 inches to 0.030 inches. Moreover, the thickness of the glue line measured between the posterior surface of the orthodontic bracket and the front surface of the tooth to which the bracket is directly bonded critically affects the magnitude of the connection forces applied to the tooth. For example, displacements of the tooth along the labial-lingual axis are normally produced by either bending the contour of the archwire to produce a force which is applied to the tooth by the bent wire or by forcing the unbent archwire into the archwire slot which has been positioned a predetermined distance from the surface of a tooth. Accordingly, it may be seen from either of the standpoints of the bond strength between the posterior surface of the orthodontic bracket and the tooth surface or from the type of orthodontic connection technique being used for straightening teeth that it has become necessary in current orthodontic practice when using the direct bonding technique to produce a glue-line having a thickness which is predetermined prior to the bonding of the bracket to the tooth surface.
In the past, the orthodontist depended largely on his own perceptive skill to directly bond the orthodontic bracket to the tooth with a glue joint having maximum strength and the proper thickness to displace the archwire slot from the archwire to insure the applying of proper correction forces. Accordingly, the attainment of a proper glue-line thickness required the expenditure of large amounts of clinical time.
Unlike the present invention, the prior art technique which depended upon the orthodontist's perceptive skills to produce a glue-line having a particular thickness did not utilize spacing elements.
U.S. Pat. No. 3,797,115 discloses an orthodontic bracket having a plurality of feet extending perpendicularly upward from the posterior surface of the bracket body which are used for retaining an adhesive which has dried prior to application of the bracket to the surface of the tooth for the final cementing of the bracket to the surface of the tooth, a fresh coating of adhesive composition is applied over the previously dried coating of cement. The bracket, including layers of dry and wet cement, is then placed directly onto the front surface of the tooth. The legs in this invention, unlike the present bracket, do not function as spacers which produce a predetermined glue-like thickness upon the cementing of the bracket body to the front surface of the tooth.